docs: def _fields_list_to_dict(fields):
      """Takes a list of field names and returns a matching dictionary.
  
      ["a", "b"] becomes {"a": 1, "b": 1}
  
      and
  
      ["a.b.c", "d", "a.c"] becomes {"a.b.c": 1, "d": 1, "a.c": 1}
      """
      for key in fields:
          assert isinstance(key, (str,unicode))
      return dict([[key, 1] for key in fields])